On Wed, Feb 29, 2012 at 09:10:07AM -0500, Edward Ned Harvey wrote: > > From: [email protected] [mailto:[email protected]] > > On Behalf Of Tracy Reed > > > > they currently have to run me 4 20A per rack. Coudldn't they cut > > that > > approximately in half (power factor correction etc, as mentioned earlier) > if I > > ran 208v? > > Depends what you call "cut it in half." > If you have a single 20A 120V circuit, as compared to a single 20A 3-phase > 208V circuit... Well, indeed you have three 120V lines bundled into the > 3-phase circuit, so it's three times as many hot wires, but it's less than > twice the effective voltage, but it's able to draw a smoother current, less > spiky, which means you're less prone to blowing circuit breakers.
so, my understanding is that you can have (or at least coresite santa clara is trying to sell me) 208v "single phase" or 208v "three phase" and the two are rather different. Now, I was refering to the 208v 'single phase' as 'split phase' earlier, which I now believe is wrong. 'split phase' refers to something similar, but the two 'legs' are 180 degrees out of phase in a 'split phase' circuit, which would give me 240v. But, my understanding is that if you have a 3 phase circuit around here, it's usually 120v per leg. each leg is 180 degrees out of phase with the others. If you want to connect a single-phase load to a 3 phase circuit (such as a server- my understanding is that all my servers have one 'hot' one 'neutral' or 'return' and one 'earthed' connector that is grounded to the case for safety.) you can either make the hot wire hot and the 'neutral' the 'neutral' of the 3 phase, giving you 120v between the 120v hot and the 0 neutral. Alternately, you can take two legs of that 3 phase circut and put the hot down the conductor on my server expecting hot, and the other hot (that is 180 degrees out of phase) in the conductor on my server expecting neutral. This means my server sees 208v, as my server, expecting single phase power, sees the difference between what it thinks is it's hot conductor, and what it thinks is it's neutral conductor. Now, what I am (perhaps incorrectly) calling single-phase 208v is usually connected to with a NEMA L6-30 twist-lock connector, which has three conductors, which I understand to be two hots and a safety earth. I'll have one of these circuits to run tests on in under a week at 55 s. market in san jose, if my insurance guy gets the paperwork to the coresite people soon. I've got two regular 'single phase' (IEC c14 plug) servers at another provider that just does co-lo on 208v single phase, I've got the PDU, the outlet to the PDU is NEMA L6-20, and from my pdu to my servers, the outlet is C13. The three-phase 208v that coresite santa clara wants to charge me more for? I believe that is three 120v hots, and therefore, rather more power than what I'm probably incorrectly refering to as 'single phase' 208v, and something I could not plug directly into my servers without buying new PSUs. Unlike the circuit that i've actually ordered, I think this '208v 3 phase' power will have a NEMA L21 plug, which is a 5 wire plug with 3 hots, one neutral and one earth. I know much less about this, as I've never tried to run a server on it. > If you're trying to reduce energy costs, the only number you need to look at > is the cost per VAh, and whatever few percent marginal PF gain you might get > by changing how you deliver your power. This is what I thought. But if you are right (and like I said, I think you are, in this case) then why is the co-lo trying to charge me exactly twice as much for a "single phase" 208v amp than for a single phase 120v amp? two amps of 120v, in a single phase system, have 32 more VA than one amp of 208v. This is the question I was starting with, and it is possible, likely even that they are charging more simply because they can. But, it's also possible, even likely, that I am misunderstanding something. _______________________________________________ Tech mailing list [email protected] https://lists.lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
